If your looking for a Shuckle that is really annoying:
1. Toxic
2. Rest
3. Gyro Ball
4. Earthquake
Holding Chesto Berry
This one will just keep using toxic to poison the enemy. Gyro Ball/Earthquake won't really do much due to his terrible attack stats.
I prefer this one and it is a real killer:
1. Substitute
2. Rest
3. Power Trick
4. Earthquake/Gyro Ball
Holding a Chesto Berry.
Use Substitute first turn, uses 1/4 of total HP but has 1 more HP than your current HP. Rest to heal, Chesto Berry will wake you up. Power Trick, switch your Attack and Defensive stats. Earthquake or Gyro Ball. Gyro Ball can have as much as 150 power max and Shuckle's speed sucks so it will do a lot. Substitute will have the same stats as Shuckle so its Defensive stats will also be good.